In a radio communication system such as a mobile phone system, exchange of signals between user equipment such as a mobile phone terminal and a radio base station is performed by radio communication that uses radio waves. In the radio communication system, a remote antenna unit (slave station apparatus, RAU) can be used, in order to extend the area over which radio communication with the user equipment is possible. Specifically, one or more slave station apparatuses are connected to a baseband unit (master station apparatus, BBU) of the radio base station, and the slave station apparatuses perform radio communication with the user equipment. The coverage area is extended by disposing such slave station apparatuses in areas where the radio waves of the radio base station do not reach. Typically, slave station apparatuses are disposed in places such as high-rise buildings, underground malls, and train stations. Slave station apparatuses (RAU) are also called optical feeder radio apparatuses or remote radio heads (RRH).
In the radio base station, each slave station apparatus and the master station apparatus are typically connected by optical fiber having low signal propagation loss. For example, Patent Document 1 discloses a radio communication system in which each slave station apparatus is connected to the master station apparatus by optical fiber. Technologies using optical fiber in this way for some of the communication channels in a radio communication system are known as ROF (Radio over Fiber) technologies.
A radio frequency signal (RF signal) from the user equipment is received by an antenna of a slave station apparatus, and then optically transmitted to the master station apparatus via an interface such an interface compliant with CPRI (Common Public Radio Interface).
In LTE (Long Term Evolution) developed by the 3GPP (Third Generation Partnership Project), OFDMA (Orthogonal Frequency Division Multiple Access) is used as the radio access system for the downlink in a radio section from the radio base station to the user equipment, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is used as the radio access system for the uplink in a radio section from the user equipment to the radio base station.